U.S. Pat. No. 3,384,023 describes an example of such a pump in which a liquid annulus is created by rotating a housing (26) within which is mounted a stationary disc (32) carrying four velocity tubes (50), each of which includes a venturi restriction (56). In each velocity tube there is an enlarged cavity (64) to the rear of the venturi restriction (56) and the cavity communicates with a passage (54). As the working liquid is rotated past each velocity tube (50) some of the liquid passes into the tube and on passing axially through the venturi restriction reduces the pressure within the cavity (64) behind the restriction due to volume changes within the tube. This causes fluid to be drawn through the the passage (54) and into the velocity tube for discharge through the end (62).
Other velocity tube devices are indicated as being usable, operating on an aspirator or jet pump principle, in place of the described nozzle-venturi combination.
Examples given are:
(1) a simple venturi tube with the suction tube (54) connected to the throat of the venturi restriction, and; PA0 (2) a tube incorporating an internal pitot tube connected to the suction tube (54).
However, all the described pumps employ suction producing devices in which the suction producing orifice is located in an internal surface of the device and suction is only achieved by causing the working liquid to pass through the device. Since the suction effect is related to flow rate and volume, the pumping speed (i.e. throughput) is severely limited due to the small flows which such velocity tube devices can accommodate.
The present invention on the other hand is concerned with a pump which whilst utilizing the interaction between a working liquid and an orifice to provide a suction effect on a fluid, does not require the working liquid to flow through an orifice to obtain the suction effect. The pump of the present invention does not therefore suffer the same pumping speed restrictions as the prior art designs do and is thereby capable of greatly increased performance and throughput.